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Using 3D hydrodynamic modeling and HSPF-WASP water quality modeling to understand spatiotemporal variations of eutrophication
Citation:
Cashel, F. AND Chris Knightes. Using 3D hydrodynamic modeling and HSPF-WASP water quality modeling to understand spatiotemporal variations of eutrophication. Coastal & Estuarine Research Foundation Conference, Portland, OR, November 12 - 16, 2023.
Impact/Purpose:
Waste Water Treatment Plants release nutrients (carbon, phosphorous, and nitrogen) into receiving waters, like rivers, lakes, and estuaries. These released nutrients can result in reduction in dissolved oxygen in the water column, growth of algae and macro-algae, and decreased water clarity. These all have ecological impacts. In this work, we are developing a three-dimensional model to simulate water quality in the Pawcatuck River Estuary (comprised of the lower Pawcatuck River and Little Narragansett Bay, which forms the western border between Rhode Island and Connecticut). By using a three-dimensional model domain, this work serves to improve our spatial understanding of the processes governing these ecological impacts, along the length of the system, with depth, and laterally, with particular interest in the spatial distribution across the bay.
Description:
Eutrophication due to anthropogenic nutrient loading has resulted in an increase in the geographic area, frequency, intensity, and duration of hypoxic events within coastal environments. Eutrophication, and additional pathways of hypoxia such as freshwater-induced stratification, phytoplankton blooms, carbonaceous biological oxygen demand, and sediment oxygen demand, exhibit dynamic spatiotemporal variation which creates difficulties in ecosystem management efforts. In this study, we use both monitoring data and mechanistic modeling to gain greater understanding of the governing mechanisms of eutrophication and hypoxia and their spatiotemporal variation in the small, complex Pawcatuck River Estuary (PRE, Connecticut/Rhode Island). High-frequency continuous and discrete water quality samples were collected from 2018-2020 along the salinity gradient and with depth to provide temporal and spatial resolution. Current research incorporates the Environmental Fluid Dynamics Code to create a three-dimensional hydrodynamic linkage to a previously developed HSPF-WASP (Hydrological Simulation Program – FORTRAN, Water Quality Analysis Simulation Program) model to assess water quality in the PRE. Here, we will present preliminary results from the modeling effort and the benefits and drawbacks of the increased spatial resolution and complexity in this approach. This study allows us to capture the spatiotemporal variation and impact of processes governing dissolved oxygen concentration, phytoplankton growth, and macroalgae blooms. The 3D model design simulates stratification and influence of sediment oxygen demand, the distribution of nutrients and carbonaceous biological oxygen demand, and the impact of macroalgae growth throughout the downstream portions of the estuary. Insights from this study provide greater understanding on the processes governing hypoxia as well as water clarity and light penetration, which limits the growth of endemic seagrass beds. Additionally, this work has the potential to inform future study and management of small, complex estuaries.
